How do I precisely specify the parameters to the Bend tool?
This tool isn't as well documented as other tools, and indeed does not call a box to adjust the last operation.
The blender manual is like &quot;yeah, it kinda works like this, just mess with it&quot;.
https://docs.blender.org/manual/en/2.80/modeling/meshes/editing/transform/bend.html
I recommend building the initial mesh with the Spin tool, to gain some control over the parameters.  It basically does a segmented extrude over an arc.
https://docs.blender.org/manual/en/latest/modeling/meshes/tools/spin.html